It is proposed to develop a repetitively pulsed (rp) hydrogen fluoride (HF) chemical laser system that is specifically designed for use in corneal microsurgery. Laser parameters such as output wavelength(s), beam quality and irradiance distribution, pulse energy, pulse duration, and pulse repetition frequency will be optimized for application in laser refractive keratectomy (LRK) and other corneal microsurgical procedures. Issues related to use in a clinical environment (such as laser size and packaging fuels and exhaust handling, EMI suppression, and beam delivery of laser radiation) will be addressed. In vitro and in vivo irradiation experiments together with post-irradiation ocular and histological examinations will be performed to optimize corneal LRK procedures, to measure the quality of tissue removal, to evaluate corneal wound healing, and to determine the quality and long-term stability of corneal optical changes induced by laser ablation. The specific aims and objectives of the proposed research are: 1) to demonstrate the formation of precise incisions and large are (up to 30 mm2) ablations of corneal surfaces using controlled and well- characterized HF chemical laser beams, 2) to measure the quality of tissue removal and the extent of adjacent tissue damage ( and inflammatory responses) at the surgical margin of resection with emphasis on the surface quality of the post-irradiated anterior stromal surface and its dependence on laser ablation parameters, 3) to determine initial and long-term corneal optical changes induced by laser ablation as a function of laser parameters, 4) to evaluate the rate and quality of epithelial and stromal wound healing as a function of laser parameters, and 5) to develop a prototype HF chemical laser system that is well suited to clinical use and well optimized for corneal ablation procedures. If Phase II research is successful, as judged by primate studies, Phase III development will commence with funding provided by Helios, HARC, HBI, and private investors. The ultimate goal of the proposed program is the development of a new clinical instrument that permits refined corneal microsurgery using safe and effective infrared chemical laser irradiation.